A tissue is said to differentiated when it has begun to synthesize characteristic macromolecules characteristic for that tissue. In some tissues, specific proteins have been well characterized, and their appearance during histodifferentiation can be monitored and assayed in minute quantities. In keratinizing epithelium the appearance of constitutive proteins during differentiation has been monitored in epidermis but not in oral epithelium. In this proposal, we plan to isolate and purify two low molecular weight, sulfur-rich proteins previously identified in rat lingual epithelium. When the proteins are obtained in relatively pure form, we shall raise antibodies to them, and by immunocytochemical techniques, seek to determine with what structural components of the cell they are associated. Furthermore, we shall attempt to determine whether these proteins are antigenically similar to proteins found in other stratified squamous epithelia of rats as well as of other mammals. These data will contribute to an understanding of the correlation between structure and biochemistry of oral epithelium. Moreover, they could form the basis for a biochemical classification of normal and pathological tissues.